CN110268483B

CN110268483B - Coaxial cable

Info

Publication number: CN110268483B
Application number: CN201880011155.1A
Authority: CN
Inventors: 平冈大生; 安达智弘; 古桥史行
Original assignee: Junkosha Co Ltd
Current assignee: Junkosha Co Ltd
Priority date: 2017-02-10
Filing date: 2018-02-06
Publication date: 2021-03-30
Anticipated expiration: 2038-02-06
Also published as: EP3582236B1; JP6924037B2; EP3582236A1; WO2018147293A1; US20200152358A1; US10825583B2; EP3582236A4; JP2018129278A; CN110268483A

Abstract

The present invention relates to a coaxial cable, and more particularly, to a small-diameter coaxial cable used in a frequency band of 100MHz or higher. An object of the present invention is to provide a coaxial cable having excellent flexibility and having a small outer diameter and excellent shielding characteristics, the object of which can be solved by: in an outer conductor of a coaxial cable, the outer diameter of a strand having the largest outer diameter (a large-diameter strand) and the outer diameter of a strand having the smallest outer diameter (a small-diameter strand) are formed by mixing strands differing by 10% or more and transversely winding them in the same direction.

Description

Coaxial cable

Technical Field

The present invention relates to a coaxial cable, and more particularly to a small-diameter coaxial cable used in a frequency band of 100MHz or higher, particularly in a frequency band of 1GHz or higher.

Background

In order to transmit a high-frequency signal through a hyperfine transmission path, it is known to use a hyperfine coaxial cable for a medical cable signal cable such as an endoscope or an ultrasonic probe cable, a notebook computer, a game machine, a signal line for robot control, and the like. In recent years, miniaturization of electronic devices has progressed, and there is a demand for improved handling of cables, and coaxial cables of finer diameter and flexibility are required. Meanwhile, a shielding property of extending a used frequency band to a high frequency band and shielding noise in a wide frequency band is required.

In order to improve the shielding property, a braided structure is used for an outer conductor of a conventional coaxial cable (patent document 1). A coaxial cable having an outer conductor of a braided structure has excellent shielding characteristics, but has problems of large friction between strands forming the outer conductor, insufficient flexibility, and poor productivity due to a large outer diameter. On the other hand, a coaxial cable provided with a transverse winding as an outer conductor of the coaxial cable has excellent flexibility, but cannot be said to be sufficient in terms of shielding characteristics for shielding noise.

On the other hand, in order to improve the shielding property while having flexibility, a transversely wound coaxial cable provided with double outer conductors has been proposed (patent document 2). Such a coaxial cable has the following problems: with the structure in which the winding directions of the transverse windings of the respective layers are different, the friction between the strands forming the outer conductor is large and the flexibility is insufficient as in the braided structure. Further, since the double transverse winding is performed, the outer diameter is increased, and the productivity is also poor.

Heretofore, a coaxial cable that can satisfy all the conditions of flexibility, stable and excellent shielding properties, reduction in diameter, and high productivity of the coaxial cable has not been realized.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 8-102222

Patent document 2: japanese laid-open patent publication No. 6-349345

Disclosure of Invention

Technical problem

The present invention has been made in view of the above problems, and an object thereof is to provide a small-diameter coaxial cable having a small outer diameter, being flexible, being usable in a small space, and having excellent shielding characteristics.

Means for solving the problems

The above object can be solved by a coaxial cable in which an insulator is covered around a center conductor and an outer conductor is provided around the insulator, characterized in that, in the outer conductor, an outer diameter of a strand having a largest outer diameter (a large-diameter strand) and an outer diameter of a strand having a smallest outer diameter (a small-diameter strand) are formed by mixing strands differing by 10% or more and transversely winding them in the same direction.

In the coaxial cable according to the present invention, since the outer conductor is formed by mixing 10% or more of strands having different outer diameters and transversely winding the strands in the same direction, the strands can be compressed without applying an excessive load to the strands, gaps are not generated between the strands, and excellent shielding properties can be obtained by suppressing leakage and intrusion of electromagnetic waves. The coaxial cable according to the present invention can be made to have a shielding characteristic superior to that of the conventional coaxial cable in which the outer conductor is of a braided structure, a double transverse wound structure, and an outer diameter smaller than that of the conventional coaxial cable in which the outer conductor is of a braided structure, a double transverse wound structure.

Further, the ratio of the outer diameters of the large-diameter strands and the small-diameter strands forming the outer conductor strands of the coaxial cable according to the present invention is preferably (outer diameter of the large-diameter strands)/(outer diameter of the small-diameter strands) 1.25 to 5.00.

The ratio of the outer diameters of the large-diameter strands to the small-diameter strands of the strands forming the outer conductor of the coaxial cable according to the present invention is (the outer diameter of the large-diameter strands)/(the outer diameter of the small-diameter strands) 1.25 to 5.00, so that the strands can be compressed particularly effectively and the shielding characteristics can be improved. Further, even when the cable is bent, no gap is generated, and the load due to friction between the strands is reduced.

Further, in the outer conductor of the coaxial cable according to the present invention, the transverse winding density represented by a ratio of a conductor shielding area, which is a sum of shielding areas of the large-diameter strands and the small-diameter strands, to a surface area of transverse winding is preferably 1.0 or more (conductor shielding area)/(transverse winding surface area).

In the outer conductor of the coaxial cable according to the present invention, 10% or more of strands having different diameters are mixed, so that the influence on the outer diameter and the appearance of the coaxial cable is suppressed, and the transverse winding density can be set to 1.0 or more. By setting the transverse winding density to 1.0 or more, no gap is generated between the strands, and the strands of the outer conductor are compressed to obtain the shielding property.

ADVANTAGEOUS EFFECTS OF INVENTION

The coaxial cable of the present invention has superior shielding characteristics to those of the conventional coaxial cable having a braided structure or a double transverse wound structure, has a small diameter and excellent flexibility, and thus can be easily wired even in a small space in a small electronic device, has high productivity as compared with the conventional coaxial cable, and can be manufactured at low cost.

Drawings

Fig. 1 is an example of a radial cross-sectional view of a conventional coaxial cable.

Fig. 2 is an example of a radial cross-sectional view of a coaxial cable according to an embodiment of the present invention.

Fig. 3 (a) is a diagram for explaining the compression efficiency of the outer conductor strand of the conventional coaxial cable, and fig. 3 (b) is a diagram for explaining the compression efficiency of the outer conductor strand of the coaxial cable according to the present invention.

Fig. 4 is a diagram for explaining the transverse winding density.

Fig. 5 is a graph showing far-end crosstalk characteristics among electrical characteristics of a multi-core transmission cable using a coaxial cable according to an embodiment of the present invention.

Fig. 6 is a graph showing a high-end far-end crosstalk characteristic among electrical characteristics of a multi-core transmission cable using a coaxial cable according to an embodiment of the present invention.

Detailed Description

Hereinafter, a coaxial cable according to the present invention will be described in detail with reference to the accompanying drawings. The embodiments described below do not limit the invention according to the claims, and all combinations of the features described in the embodiments are not necessarily essential to implementing the invention.

Fig. 1 is a radial cross-sectional view of an example of a conventional coaxial cable, in which an outer conductor 15 is formed by covering the outer periphery of a center conductor 11 with an insulating layer 12 and laminating a first layer transverse winding 13 and a second layer 2 transverse winding 14 on the outer periphery thereof. The conventional coaxial cable 10 is formed of strands having the same outer diameter in each layer as the strands forming the outer conductor 15. When the outer conductor 15 is formed by two-layer transverse winding, the outer diameter increases, it is difficult to eliminate the possibility of gaps being generated between the strands of the outer conductor when bent, and flexibility is also reduced.

The present inventors have found that, unlike conventional transverse winding, in the outer conductor, the outer diameter of the strand having the largest outer diameter and the outer diameter of the strand having the smallest outer diameter are formed by mixing strands differing by 10% or more and transversely winding them in the same direction, so that the shielding characteristics can be improved over conventional coaxial cables and the diameter can be reduced.

As shown in fig. 2, in the coaxial cable 20 according to the present invention, an insulator 22 is covered around a center conductor 21, and an outer conductor 25 is provided around the insulator 2. In the outer conductor, the outer diameter of the strand (large diameter strand) 24 having the largest outer diameter and the outer diameter of the strand (small diameter strand) 23 having the smallest outer diameter are formed by mixing strands differing by 10% or more and transversely winding them in the same direction. The outer diameter of the strands of the outer conductor 25 may be two, three, or more.

The center conductor 21 of the coaxial cable 20 according to the present invention is formed of a stranded plurality of silver-plated copper alloy wires. The center conductor 21 may be formed of a copper wire or a copper alloy wire, a blister copper, or the like plated with tin, silver, nickel, or the like, in addition to the copper alloy wire. When a twisted wire is used for the center conductor 21, the twisted wire is preferably used because it is difficult to cut the wire because of excellent flexibility as compared with a single wire, particularly in the case of using a thin-diameter wire. A single wire may be used for the center conductor 21. When using a single wire to the cross-sectional area of the conductor, the outer diameter can be made smaller than a litz wire.

As the central conductor 21 of the coaxial cable 20 according to the present invention, a conductor having a small diameter of not less than American Wire Gauge (AWG) 36 is used. For example, in the case of using the silver-plated copper alloy wire of AWG40 as the center conductor 21 of the coaxial cable 20, 7 strands of silver-plated copper alloy wire having an outer diameter of 0.03mm were twisted into a silver-plated copper alloy wire having an outer diameter of 0.09 mm. The effect of the invention is better for the thin-diameter coaxial cable.

The insulator layer 22 of the coaxial cable 20 according to the present invention is formed of tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA). The insulator layer 22 may be formed of polyolefin such as polyethylene, tetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), or the like. The thickness of the insulator layer 22 is determined by the outer diameter of the center conductor 21 to have a predetermined resistance.

The outer conductor 25 of the coaxial cable 20 according to the present invention is used by mixing strands having outer diameters different by 10% or more. Silver-plated soft copper wire is used for the large-diameter strands 24, and silver-plated hard copper wire is used for the small-diameter strands 23. Which is wound laterally in the same direction along the outer periphery of the insulator layer 22. For example, 19 strands of silver-plated soft copper wire having an outer diameter of 0.04mm and 8 strands of silver-plated hard copper wire having an outer diameter of 0.02mm are mixed and wound around the outer periphery of the insulator layer 22 having an outer diameter of 0.24mm in the same lateral direction. In addition to the above, the strands of the outer conductor 25 may be formed of copper wires, copper alloy wires, or blister copper, which are plated with tin, silver, nickel, or the like.

Preferably, the strands of the outer conductor 25 are wound around the insulator layer 22 in the transverse direction at an angle of 18 ° to 40 °, and the winding direction is not limited to the left winding or the right winding. For example, after winding the outer peripheral surface of the insulator layer 22 at an angle of 25 °, the outer conductor 25 is compressed by passing through a 0.33mm die. Since the strands having the difference of the outer diameters of 10% or more are mixed, the compression between the strands can be effectively performed, and the contact between the strands is changed from the line contact to the surface contact, so that the coaxial cable having the excellent shielding characteristic can be provided.

After the strands of the outer conductor 25 are transversely wound, the strands are compressed as they pass through the die. By the strands being compressed, the contact between the strands changes from line contact to surface contact and the gaps between the strands become smaller. Even when the coaxial cable 20 is bent, the compressed strands are not slit, so that a stable shielding effect can be obtained. At this time, in the transversely wound strands, the compressive force applied from the upper portions of the strands is effectively transmitted to the strands, and thus the strands can be compressed, as compared to the outer conductor of the conventional coaxial cable formed of only strands of the same outer diameter. In the case where the difference in the outer diameters of the large-diameter strands and the small-diameter strands is 10% or more, there is an effect of suppressing part of the strands from being pushed up from the surface of the insulator when the strands are compressed. In particular, when the ratio of the outer diameters of the large-diameter strands to the small-diameter strands is (the outer diameter of the large-diameter strands)/(the outer diameter of the small-diameter strands) 1.25 to 5.0, the effect of effectively transmitting the compressive force applied from the transversely wound outer periphery to between the strands is excellent. Further, it is easy to be accommodated in the gap of the strand, and while improving the compression efficiency, the outer diameter of the coaxial cable is prevented from becoming large, and the reduction of the shielding effect caused by the deviation of the strand due to the bending of the cable is prevented. When the ratio of the outer diameters of the large-diameter strands to the small-diameter strands is greater than 5.0, the strands of the thin wire fall into the gaps of the large-diameter strands, and the effect of effectively transferring the compression ratio is reduced.

Fig. 3 is a diagram for explaining a compressive force transmitted to the strands when a compressive force is applied to the outer conductor. Fig. 3 (a) is a diagram of the case of an outer conductor of a conventional coaxial cable using only strands having the same outer diameter, and fig. 3 (b) is a diagram of the case of an outer conductor of a coaxial cable according to the present invention in which a large-diameter strand and a small-diameter strand are mixed. Hereinafter, the efficiency (compression efficiency) of transmitting the compression force of (a) and (b) to the strands will be described with reference to fig. 3.

(a) Efficiency of compression of

When a compressive force Na is applied from the outer peripheries of the large-

diameter strands

321, 322, 323 which are wound around the outer periphery of the insulator 31 in the transverse direction, a compressive force Fa acting between the

strands

322, 323 is obtained.

The component of the compressive force Na in the direction perpendicular to the tangent Ta of the strand 322 and the strand 323 corresponds to the compressive force Fa. The compressive force Fa is shown below.

Fa ═ Nacos α (formula 1)

(b) Efficiency of compression of

When the compressive force Nb is applied from the outer peripheries of the large-

diameter strands

341, 342, 343 and the small-diameter strands 351 which are wound around the outer periphery of the insulator 33 in the transverse direction, the compressive force Fb acting between the

strands

342 and 343 is obtained.

A compressive force Nb is first applied to the strands 351 located at the outermost periphery of the transverse winding. The component of the compressive force Nb in a direction perpendicular to the tangent Tb1 of the

strands

351 and 342 corresponds to the compressive force Fb1 applied to the strands 342. The component of the compressive force Fb1 in the direction perpendicular to the tangent Tb2 of the

strands

342 and 343 corresponds to the compressive force Fb acting on the strands 343.

The compressive force Fb is shown below.

Fb1＝Nbcosα

Fb1cos β Nbcos α cos β (formula 2)

In the conventional coaxial cable of (a), when the strand having an outer diameter of 0.03mm is used as the outer conductor, the compression efficiency obtained from the above equation is 11.1, and in the coaxial cable of the present invention of (b), when the strand having an outer diameter of 0.03mm and the strand having an outer diameter of 0.021mm are used in a mixture, the compression efficiency obtained from the above equation is 60.8. It can be seen that the compression efficiency is higher when the strand diameters are used mixedly. The conductor can be compressed without applying a large load to the outer conductor surface, and even in the case of using an ultrafine wire, processing can be performed without causing breakage of the strand during manufacturing.

The outer conductor of the coaxial cable according to the present invention can provide the coaxial cable with excellent shielding characteristics by having a transverse winding density of 1.0 or more. The method of finding the transverse winding density is explained with reference to fig. 4. The transverse winding density is represented by the ratio of the conductor shield area to the transverse winding surface area. The symbol D in FIG. 4 represents the average diameter of transverse winding, and the outer diameter of the insulator and the outer diameter D of the transverse wound strand can be determined_wAnd (4) summing. The transverse winding surface area of the coaxial cable of length P is represented by P x pi D. The conductor shielding area refers to the area covered by the transverse winding strand in the transverse winding surface area, wherein the number of the transverse winding strand is n, and the outer diameter of the transverse winding strand is d_wThe conductor shield area was obtained as follows.

Mathematical formula 1

Therefore, the transverse winding density can be obtained by the following equation.

Mathematical formula 2

In the outer conductor of the coaxial cable of the present invention, transversely wound strands having different outer diameters are mixed. Therefore, the transverse winding density of the outer conductor of the coaxial cable of the present invention is obtained by determining the transverse winding density for each strand diameter of the large-diameter strands and the small-diameter strands and adding them to obtain the transverse winding density of the coaxial cable.

The conventional coaxial cable has an outer conductor wound in a transverse direction with a transverse winding density of about 0.95 to 0.98 in consideration of the fluctuation of the outer diameter of the insulator. When the transverse winding density is more than 1.0, part of the outer conductor strands are pushed up due to a problem that causes thickening of the outer diameter or the like, making the appearance unattractive. On the other hand, in the outer conductor of the coaxial cable of the present invention, since the strands having an outer diameter different by 10% or more are mixed, the conductor is hard to be pushed up, and even if the transverse winding density is 1.0 or more, the outer diameter is hard to be affected.

In the coaxial cable according to the present invention, a PFA sheath layer may be provided around the outer conductor. The sheath layer may be formed of polyethylene, polyester, polyimide, or tetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), or the like.

In the coaxial cable according to the present invention, the multicore cable is formed by twisting a plurality of coaxial cables. A jacket layer is formed on the outer circumference of the stranded multi-strand coaxial cable to form a transmission cable.

The present invention is illustrated in detail by the following examples. The following examples are intended to illustrate the invention, the content of which is not limited to the following examples.

Examples

The coaxial cables are prepared so that the characteristic impedances are substantially equal, and the far-end crosstalk is measured by changing the frequency of the transmission signal of the two-core parallel cable as a parallel two-core. Since the crosstalk is suppressed, the shielding characteristic of the coaxial cable can be confirmed.

(example 1)

As the center conductor, a conductor of AWG40 (7 strands of silver-plated copper alloy wire having an outer diameter of 0.03mm were stranded as a conductor having an outer diameter of 0.09 mm) was used, PFA was extruded as an insulator layer, and the thickness was 0.075mm and the outer diameter was 0.24 mm. 24 strands of 0.03mm strand diameter silver plated annealed copper wire and 8 strands of 0.021mm strand diameter silver plated hard copper wire were mixed and the outer circumference of the insulator layer was wound transversely through a 0.31mm die to form an outer conductor. PFA having a thickness of 0.03mm was extruded at the outer periphery of the outer conductor to manufacture a coaxial cable. A two-core parallel cable was manufactured using the coaxial cable, and far-end crosstalk was measured.

(example 2)

A coaxial cable was manufactured, a two-core parallel cable was manufactured, and far-end crosstalk was measured in the same manner as in example 1, except that 10 strands of silver-plated soft copper wire having a strand diameter of 0.04mm and 8 strands of silver-plated hard copper wire having a strand diameter of 0.021mm were mixed and an outer conductor was transversely wound.

(example 3)

A coaxial cable was manufactured, a two-core parallel cable was manufactured, and far-end crosstalk was measured in the same manner as in example 1, except that 22 strands of silver-plated soft copper wire of 0.03mm strand diameter, 3 strands of silver-plated stiff copper wire of 0.021mm strand diameter, and 8 strands of silver-plated stiff copper wire of 0.016mm strand diameter were mixed and an outer conductor was transversely wound.

(example 4)

A coaxial cable was manufactured, a two-core parallel cable was manufactured, and far-end crosstalk was measured in the same manner as in example 1, except that 13 strands of silver-plated soft copper wire of 0.04mm strand diameter and 25 strands of silver-plated hard copper wire of 0.021mm strand diameter were mixed and an outer conductor was transversely wound.

(example 5)

As the center conductor, a conductor of AWG44 (7 strands of silver-plated copper alloy wire having an outer diameter of 0.02mm stranded as a conductor having an outer diameter of 0.06 mm) was used, and PFA was extruded as an insulator layer to have a thickness of 0.05mm and an outer diameter of 0.16 mm. 18 strands of 0.03mm strand diameter silver plated annealed copper wire and 5 strands of 0.016mm strand diameter silver plated hard copper wire were mixed and the outer circumference of the insulator layer was wound transversely through a 0.23mm die to form the outer conductor. PFA having a thickness of 0.03mm was extruded at the outer periphery of the outer conductor to manufacture a coaxial cable. A two-core parallel cable was manufactured using the coaxial cable, and far-end crosstalk was measured.

(example 6)

As the center conductor, a conductor of AWG48 (7 strands of a silver-plated copper alloy wire having an outer diameter of 0.013mm was stranded as a conductor having an outer diameter of 0.038 mm) was used, and PFA was extruded as an insulator layer to a thickness of 0.026mm and an outer diameter of 0.09 mm. 16 strands of 0.021mm strand diameter silver plated annealed copper wire and 4 strands of 0.016mm strand diameter silver plated hard copper wire were mixed and the outer circumference of the insulator layer was wound transversely through a 0.15mm die to form the outer conductor. PFA having a thickness of 0.025mm was extruded at the outer circumference of the outer conductor to manufacture a coaxial cable. A two-core parallel cable was manufactured using the coaxial cable, and far-end crosstalk was measured.

Comparative example 1

As the center conductor, 7 strands of a silver-plated copper alloy wire having an outer diameter of 0.02mm were stranded as a conductor having an outer diameter of 0.06mm, and PFA was extruded as an insulator layer to have a thickness of 0.05mm and an outer diameter of 0.16 mm. 18 strands of 0.03mm strand diameter silver-plated annealed copper wire was wound transversely around the outer periphery of the insulator layer, and 24 strands of 0.03mm silver-plated annealed copper wire were wound transversely in the same direction around the outer periphery thereof to form an outer conductor. PFA having a thickness of 0.025mm was extruded at the outer circumference of the outer conductor to manufacture a coaxial cable. A two-core parallel cable was manufactured using the coaxial cable, and far-end crosstalk was measured.

Comparative example 2

A coaxial cable was manufactured, a two-core parallel cable was manufactured, and far-end crosstalk was measured in the same manner as in example 1, except that 11 strands of silver-plated soft copper wire having a strand diameter of 0.04mm and 22 strands of silver-plated hard copper wire having a strand diameter of 0.021mm were mixed and an outer conductor was transversely wound.

Comparative example 3

A coaxial cable was manufactured, a two-core parallel cable was manufactured, and far-end crosstalk was measured in the same manner as in comparative example 1, except that 12 strands of 0.03mm strand diameter silver-plated soft copper wire and 12 strands of 0.016mm strand diameter silver-plated hard copper wire were mixed and an outer conductor was transversely wound.

Examples and comparative examples are shown in table 1.

TABLE 1

The far-end crosstalk of each example and each comparative example was measured by a Vector Network Analyzer (VNA).

Fig. 7 is a graph showing the far-end crosstalk characteristics in the electrical characteristics of the coaxial cables of the comparative examples and examples in which the conductor of AWG40 is used as the center conductor, the horizontal axis represents the frequency of the transmission signal, and the vertical axis represents the gain. Fig. 8 is a diagram similarly showing the far-end crosstalk characteristics of coaxial cables of examples and comparative examples in which AWG44 or larger conductors are used as the center conductors. As shown in table 1, fig. 7, and fig. 8, in the examples, the outer conductor outer diameter was smaller than that of the conventional coaxial cable as compared with the conventional coaxial cable as shown in the comparative example, and it was confirmed that the crosstalk per frequency was sufficiently suppressed as compared with the conventional coaxial cable, and thus the shielding characteristics were excellent. The coaxial cable of the comparative example is not compatible with the shielding property and the diameter reduction.

Industrial applicability

The small-diameter coaxial cable of the present invention is applicable to medical cables, signal cables for controlling notebook computers, game machines, robots, signal transmission cables, and the like.

Description of reference numerals

10: existing coaxial cables; 20: the coaxial cable of the present invention.

Claims

1. A coaxial cable in which an insulator is covered around a center conductor and an outer conductor is provided around the insulator,

in the above-described outer conductor, the outer diameter of the strand having the largest outer diameter (large diameter strand) and the outer diameter of the strand having the smallest outer diameter (small diameter strand) are formed by mixing strands differing by 10% or more and transversely winding them in the same direction,

in the outer conductor, a transverse winding density represented by a ratio of a conductor shielding area to a transverse winding surface area, which is a sum of shielding areas of the large-diameter strands and strands other than the large-diameter strands, is 1.0 or more (conductor shielding area)/(transverse winding surface area).

2. The coaxial cable according to claim 1, wherein a ratio of an outer diameter of the large-diameter strand to an outer diameter of the small-diameter strand in the strands forming the outer conductor is 1.25 to 5.00 (outer diameter of the large-diameter strand)/(outer diameter of the small-diameter strand).

3. The coaxial cable according to claim 1 or 2, wherein the american wire gauge value of the center conductor is 36 or more.